The field of the disclosure relates generally to a blowout preventer (BOP) for oil and gas wells, and more particularly, to a variable ram for a BOP.
Most known BOPs mount on top of a wellhead and provide a means to regulate the pressure of a wellbore. Variable bore rams typically include a pair of rams on opposing sides of a BOP stack that actuate to form a sealed arrangement with a drill pipe. When the variable bore rams are actuated radially inward, the inner most bore face contacts the outer surface of a drill pipe and forms a sealing arrangement. Some known variable rams include metallic inserts and elastomer packers that cooperate as a coherent unit to create a seal across drill pipes of different sizes.
Some known designs for variable bore rams incorporate a stiffer material along a bore contact surface. Generally, at high temperatures and high pressures, these rams undergo large deformation across the bore contact surface, face recess, and other critical regions of the packer, resulting in a breakdown of the stiffer material and a reduction of service life of the ram. In order to improve the service life of the ram, reinforcing filler materials such as elastomers would need to have both a large modulus of elasticity and a large elongation capacity. However, these two requirements typically conflict with each other because the addition of reinforcing filler materials typically improves one property at the cost of the other.
Many known designs that add a stiffer material on the bore contact surface do not help facilitate decreasing deterioration of the bore contact surface as the material undergoes significant deformation. Because the stiffer materials tend to have a lower elongation capacity, they typically do not facilitate large deformation.